The summer heat had not hit its suffocating peak in the Central Valley's tomato fields when Olivia Tamayo's supervisor approached her during a break.

He needed her to work in another area of the 15,000-acre farm, he said. In the company truck, he drove so fast along the dirt road that it jostled Tamayo around in the cab. As he sped into an unfamiliar stand of almond trees, she asked him where he was going. He stopped deep in the orchard labyrinth.

"You're going to be mine," she remembers him saying. The crew boss showed Tamayo that he was carrying a handgun. He placed it on the dashboard. Then he raped her, she said.

Despite Tamayo's accusation that the supervisor, Rene Rodriguez, would rape her twice more, no criminal charges were filed, and Rodriguez repeatedly denied the claims.

But in what would become a landmark case, the federal government filed a civil sexual harassment lawsuit against Tamayo's employer, Harris Farms, one of the nation's largest agribusinesses and owner of a popular restaurant along Interstate 5. In 2004, Tamayo's case was the first federal sexual harassment lawsuit against a grower to reach a trial.

A jury found that the company failed to curb the sexual abuse and then retaliated against Tamayo for complaining. It awarded Tamayo nearly $800,000.

Since then, there have been few signs that conditions have gotten better for farmworkers in California - or elsewhere in the U.S.

In partnership with PBS' "Frontline" and television network Univision, reporters spent nearly a year reviewing thousands of pages of documents and crisscrossing the nation to hear workers' stories of sexual assault.

The investigation was the first systematic analysis of the 41 lawsuits filed by the U.S. Equal Opportunity Commission against agricultural businesses in the last 15 years.

In virtually all of the lawsuits, the alleged perpetrators held positions of power in the company; in more than half of the lawsuits, the superiors were accused of targeting multiple victims. In cases in which sexual assault and rape are alleged, these supervisors remained on the job for years without fear of arrest, and law enforcement has done almost nothing to prosecute potential crimes.

More than four of five workers who reported the problem to their employers say they were demoted, fired or subjected to further abuse, the analysis shows.

The lawsuits emerged from 1,106 sexual harassment complaints filed by agricultural workers with the Equal Employment Opportunity Commission since 1998. Most of the complaints are dismissed by the federal commission or settle out of court, and the details remain secret.

In May, the California Agricultural Labor Relations Board, which enforces state labor laws for farmworkers, filed its first case related to sexual harassment, deciding to make the issue a priority because it wasn't being adequately addressed. In that case, a woman harvesting sweet potatoes in Stanislaus County filed claims that she was fired after accusing a supervisor of sexually assaulting her.

Prosecutors didn't take up Olivia Tamayo's case. And years after the jury verdict, her former employer, Harris Farms, has continued to deny any wrongdoing. The workers had a consensual relationship that the company did not know about, CEO John Harris said in a statement. Although the jury believed the accused employee was a supervisor, "we felt he was not," Harris said.

The Equal Employment Opportunity Commission, which is charged with enforcing workplace civil rights laws, is the only government entity actively pursuing these cases. But it cannot bring criminal charges. It can file only civil lawsuits against the employers - not the perpetrators - for failing to stop on-the-job sexual harassment.

The California Agricultural Labor Relations Board had never filed a complaint related to sexual harassment until May.

In the May case, Elvia Hernandez, who harvested sweet potatoes for Sandhu Brothers Poultry & Farming in Stanislaus County, said a supervisor sexually harassed her by masturbating repeatedly in front of her, offering to pay her for sex and forcibly kissing her. Hernandez claims that after she reported the harassment, she was fired.

An attorney for the company, a small family farm, said he believes sexual harassment is "not an area where the ALRB (Agricultural Labor Relations Board) should be involved with." The attorney, Jakrun Sodhi, called the allegations "specious."

This story was produced by The Center for Investigative Reporting as part of a collaboration with Univision, PBS' "Frontline" and the Investigative Reporting Program at the UC Berkeley Graduate School of Journalism. Learn more at cironline.org. E-mail the reporters: byeung@cironline.org and grace@gracerubenstein.com.